The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools.
Combustion tools are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 6,145,724, all of which are incorporated by reference herein.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include inserting the fuel into the combustion chamber, mixing the fuel and air within the chamber and removing or scavenging combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original or pre-firing position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
An operational problem of conventional combustion-powered tools is that as air required for combustion enters the tool, due to the relatively dirty operational environment of such tools, dirt, dust and/or other debris, including but not limited to fragments of nail collation material, sawdust, wallboard particles and the like enters the tool, specifically the cylinder below the piston. This contaminated air enters mainly through air ports located below the exhaust ports as the piston returns to its pre-firing position after combustion. These air ports are typically located below or in close proximity to a shock-absorbing bumper located within the cylinder. Air cannot reenter through the exhaust ports due to the presence of one-way petal valves. Through prolonged tool operation, among other effects, these contaminants deteriorate tool lubricants required for smooth operation of the piston and movement of the reciprocating valve sleeve, the component used to close the combustion chamber.
Such tools typically have an air filter located at an upper end of the tool near the combustion chamber fan air intake. However, this filter has been designed to filter air entering the combustion chamber and has no effect on the air located below the piston in the cylinder, where contaminant-caused damage has been known to occur. It has been previously difficult to place a filter in the tool for removing contaminants from air located below the piston because of space considerations, and due to relatively high operational temperatures (in the order of 300° F.) which degrade many filter materials. Also, the size of any such filter would necessarily be relatively large to permit the passage of sufficient air to maintain proper air circulation within the tool. As such, space, material and tool operational factors combine to discourage tool designers from placing a filter on the tool to filter the air in the cylinder below the piston.
Thus, there is a need for a combustion-powered fastener-driving tool in which air located below the piston is filtered to remove contaminants encountered in the course of normal tool operation. There is also a need for such a filter which can withstand tool operational temperatures, and which maintains acceptable tool air circulation patterns.